Measuring devices, such as shaft encoders for determining angular positions of moving axes or shafts by contactless single or multiturn sampling, are already generally used for monitoring and controlling mechanical motion sequences. Shaft encoders are, for example, employed for detecting the speed of motors and controlling the same, for the open-loop or closed-loop control of transport systems, or for monitoring conveyor belts. However, recently the demands on the accuracy, and in particular on the reliability, of the shaft encoders have considerably increased to be able to satisfy current safety standards and controlling tasks in plant and mechanical engineering applications.
In the applications of shaft encoders which are sometimes very demanding as regards ambient conditions, soiling and/or wear effects can result in non-tolerable faulty measurements or even a partial or total failure of a shaft encoder. Therefore, it is imperative to improve the reliability of existing shaft encoder systems, however not without taking into consideration economic and constructional conditions.
In prior art, two-channel shaft encoder systems are known which use two separate measuring means for one and the same shaft to increase safety by a redundant measurement of the angle of rotation. The technical efforts as well as the costs for a shaft encoder system are naturally significantly increased thereby. Moreover, the incorporation of several housings for individual measuring means can be constructionally disadvantageous or even impossible.
It is therefore an object underlying the present invention to provide a shaft encoder device showing increased reliability of the measured values obtained, at the same time maintaining a construction as simple as possible and as little impeding as possible with units that can be incorporated as simply as possible and in a manner as little impeding as possible.